Allow reference of existing context
...without creating a new part
Support shortInstrumentName
Support for staff groups
Continue restructure
Avoid doubled looping
More restructuring
Support group name
Support for nested groups
Support of more staff types
Avoid double barlines
Fix multiclef regression
Preparing for non-default part-group symbols
hopefully fix #486
Merge pull request #487 from PeterBjuhr/musicxml

Musicxml Export wip
implement showing at least n lines of context when jumping to another location

wish issue #488
pref for number of contextual lines to show, implement and close #488
improve pref page layout
let autocompile jobs finish, fix #120
update chlog, pot and nl
return None when no actions are existent

circumvent and close #483